1. Field of the Invention
Exemplary embodiments of the present invention relate to a charging and discharging control apparatus of a DC link capacitor in an electric power steering relay and a method thereof, and more particularly, to a charging and discharging apparatus of a DC link capacitor in an electric power steering relay, in which the DC link capacitor turning-on the electric power steering relay includes at least two switching elements charged or discharged by a collector current so as not to relay on an internal temperature, facilitates a circuit design, and meets an electronic control system using software, and a method thereof.
2. Description of Related Art
An electric control unit (ECU) in an electric power steering (EPS) is connected to a relay for fail-safety of units, and charges a DC link capacitor which is located at a latter stage of the relay so as to prevent a burning of the relay due to an inrush current when the relay is turned-on.
In this case, in order to prevent the burning of the relay due to overcharging of the DC link capacitor, the DC link capacitor needs to be completely discharged, prior to being charged.
FIG. 1 is a circuit diagram illustrating a charging-discharging control apparatus 10 of a DC link capacitor in an electric power steering relay in accordance with the related art.
Referring to FIG. 1, the charging-discharging control apparatus 10 of a DC link capacitor in an electric power steering relay in accordance with the related art includes a charging switch Q2 and a discharging switch Q3 for a DC link capacitor C, a control unit 2 configured to control the charging switch Q2 and the discharging switch Q3 using a PWM signal, and a resistor unit 4 configured to control a charging-discharging time, along with the DC link capacitor C. In this case, a capacitance of the DC link capacitor C is determined depending on a maximum current of the ECU and a time constant thereof is determined depending on a circuit design.
That is, since the capacitance of the DC link capacitor varies depending on the current capacity of the current ECU, the charging and/or discharging resistance values within the circuit are set differently and since the charging/discharging current amount may not be determined, the charging time and the discharging time are set for each ECU in a lump.
However, the related art has the following problems.
First, when the maximum current of the ECU is increased, the capacitance of the DC link capacitor is increased and thus the resistance value is reduced to keep the same time constant, thereby making it difficult to design a circuit.
Second, when the internal temperature of the ECU rises, power is reduced at the resistor unit, such that a resistor having a high power factor needs to be used. To this end, the related art uses a method of increasing power while reducing the resistance value, by configuring the resistor unit in which at least two resistors are connected to each other in parallel.
The related art is difficult to design a sharing circuit, needs to additionally connect a resistor as the internal temperature of the ECU is increased, and does not meet an electronic control system which applies preset time constants in a lump using software.
Finally, the related art may not cope with the change in the internal temperature of the ECU on which the DC link capacitance relies, such that the DC link capacitor may be overcharged at low temperature and undercharged at a high temperature.